Method of making memory devices

ABSTRACT

A method for making an optical memory storage medium which has a transparent substrate with void cells of empty spaces and ablative material on the cell walls is disclosed. In one example, a base plate is coated with a masking layer. Pits are formed on the plate by mechanically stamping the masking layer and the base plate with a punch. A layer of ablative material is next applied on the pitted plate. The masking layer is then removed, together with any ablative material on it. The base plate is joined with a cover plate that seals the top of the pits to form void cells. In another example, a base plate is coated with a photo resist. The photo resist is exposed and developed. Pits are formed on the plate by etching the uncovered areas of the base plate. This is followed by the application of ablative material and the removal of the photo resist. The base plate is joined with a cover plate that seals the top of the pits to form void cells.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 750,733, filed July 1,1985, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to an optical memory device disclosed in aseparate U. S. patent application by the applicant, titled MEMORYDEVICE, Ser. No. 06/392,147, filed June 25, 1982, now pending.

The memory device comprises a substrate having a plurality of void cellswith empty spaces. Each void contains a certain amount of ablativematerial deposited on its wall. The substrate is transparent to thelight used for reading and writing of the information. The cells, orbubbles, with empty spaces of certain shape, are embedded in thesubstrate. The ablative material is opaque to the light used for readingand writing of the information. The ablative material can be vaporizedby a high intensity light beam during a write operation.

The distribution of the ablative material on the cell wall determinesthe content of the information stored. During a read operation, a lowintensity light beam is directed towards the cell to detect the patternof distribution of the ablative material. During a write operation, ahigh intensity light beam is directed towards the cell to vaporize andredistribute the ablative material.

In one embodiment of the memory device, a cell is used to store one bitof information. The cell is made in an elongated shape with its middleslightly constricted. When a bit of information is stored, one end ofthe cell has the ablative material covering its wall and the other endis clear of the ablative material. A binary one or zero is storeddepending on which end is covered or clear. To read the information, alow intensity light beam is directed towards one particular end of thecell. A light sensor downstream of the light beam is used to detect thecontent of the information. To change the content of the informationpreviously stored, a high intensity light beam is directed towards theend covered with ablative material. The light beam is of sufficientintensity so that the ablative material is vaporized. The vaporizedmaterial diffuses to the other end and is then allowed to cool down anddeposit on its wall. As a result, a binary zero is changed to a one orvice versa. FIG. 1 illustrates such an embodiment. A substrate 21 ismade as a plate. A cut on the plate exposes one half of a cell. The cellhas two ends 23 and 24 joined by a narrower section. The two endsrepresent the numbers 0 and 1. If the end 23 is clear and the end 24 iscovered, the number 0 is stored. If the end 24 is clear and the end 23is covered, the number 1 is stored. A light beam 22 is shown directedtowards the lower end of the cell. The plate in this figure is shownfacing the left.

This invention discloses a method for making the memory device of thetype disclosed.

An important property of a mass memory device is its ability to store alarge amount of information in a given surface area of the recordingmedium. To achieve a high density of information in the memory devicerefered to above, small cell size is required. A suitable amount ofablative material should also be sealed in each cell. An object of thisinvention is to disclose a method for making the memory device withsmall cells and with controllable amounts of ablative material sealed inthem. Another object is to make the memory device with cells ofdesirable shape and at preselected locations. Still another object ofthe invention is to disclose a method that is suitable for massproduction of the memory device.

BRIEF SUMMARY OF THE INVENTION

The material chosen for the substrate may be glass or plastic. Theablative material may be metal, iodine, phosphorus, inorganic compound,or organic compound that is easily vaporized by a high intensity lightbeam. It is preferable to choose an ablative material with itsvaporization temperature lower than the melting point of the substrate.

Several examples of the method are described in this specification. Theexamples involve some common steps which will be outlined as follows.More detail description of the method will be given later.

The main structure of the memory device is made by joining two platestogether. Before the plates are joined, one of them have pits withablative material deposited in them. The pits form the memory cellsclose to the boundary of the two plates when they are joined. The twoplates will be called the base plate and the cover plate respectively.In a typical application, the memory device is made as a circular diskwith a hole in the middle which can be engaged with a spindle.

The method involves three basic steps. The first step prepares the baseplate of the substrate. Initially, the base plate of the substrate has aflate surface. A masking layer is coated on top of it. FIG. 2 and 3 showthe base plate coated with the masking material. FIG. 2 is a perspectiveview of a portion of the coated base plate. FIG. 3 is a cross sectionalview of the same portion of the coated base plate. Shown in the figuresare the base plate 1 and the masking layer 2. The plate in FIGS. 2 and3, as well as those in the rest of the drawings, are shown facing up.Pits at the desired locations for the memory cells are formed byremoving or displacing parts of the masking material and the base plate.As will be disclosed in more details later, the pits can be formed inmore than one ways, such as stamping and etching. FIGS. 4 and 5 show thebase plate of the substrate with pits formed on it. FIG. 4 is aperspectiive view of a portion of the pitted base plate. FIG. 5 is across sectional view of the same portion of the base plate. Shown inFIG. 4 are the base plate 1, the masking layer 2, and the pits 3. Thepit in the front is shown cut in half for illustration purpose. Shown inFIG. 5 are the base plate 1, the masking layer 2, and the pit 3.

The second step involves the application of the ablative material andthe removal of the masking layer. The base plate prepared in the firststep is coated with the ablative material. The coated base plate isshown in FIG. 6. The figure shows the cross sectional view with the baseplate 1, the masking layer 2, the pit 3, and the ablative material 4.The masking layer is then removed, together with any ablative materialthat may have been coated on it. This leaves the base plate of thesubstrate with the pits and the ablative material in the pits. FIG. 7shows the base plate 1, the pit 3, and the ablative material 4 at theend of this step. As will be disclosed in more details, variations arepossible in the coating and the removal processes.

The third step involves joining or uniting the base plate of thesubstrate with the cover plate of the substrate. The top of the pit isthus sealed by the cover plate. The covered pit forms the empty cellwith ablative material in it. This completes the construction of thememory device. FIG. 8 shows a cross section of a portion of thecompleted memory device. Shown in the figure are the base plate 1, theablative material 4, the cover plate 5, and the empty cell 6. Details ofthe third step again vary and will be disclosed later.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of the memory device for storage of binaryinformation.

FIG. 2 and 3 show a base plate coated with a masking layer.

FIG. 4 and 5 show the base plated with pits formed on it.

FIG. 6 shows the base plate with ablative material applied.

FIG. 7 shows the base plate with the masking layer removed.

FIG. 8 shows the completed device with the base plate and the coverplate joined.

FIG. 9 shows a punch used to stamp a base plate.

FIG. 10 shows the punch and the base plate stamped.

FIG. 11 shows another punch used to stamp a base plate.

FIG. 12 shows the punch and the base plate stamped.

FIG. 13 shows the base plate with the masking layer.

FIG. 14 shows a cover plate with spacers.

FIG. 15 shows a completed device with the base plate and the cover platejoined.

FIG. 16 shows a pitted base plate with binding agent and a maskinglayer.

FIG. 17 shows the base plate with ablative material applied.

FIG. 18 shows the base plate with the masking layer removed.

FIG. 19 shows the completed device with the base plate and the coverplate joined.

DETAILED DESCRIPTION OF THE METHOD

Each step described above can be done in more than one ways. Thefollowings are examples of making the memory device based on the threesteps.

EXAMPLE 1

A plastic plate is prepared with a flat surface. The plate is coatedwith a thin layer of masking material. The masking material ispreferable softer than the plastic plate. The masking material issolvable in a solvent to be used later in the second step. The coatedbase plate is shown in FIGS. 2 and 3.

A stamping punch is made of a hard metal with protrusions on it. Thelocation and the shape of the protrusion correspond to the pit to beformed on the base plate. The punch is shown in FIG. 9 with body 7 andprotrusion 8. The protrusion in the front is shown cut in half forillustration purpose. The punch is shown facing up.

The punch is then pressed on the plastic plate. Sufficient pressure isapplied so that the protrusion on the punch penetrates the masking layerand further displaces the plastic underneath. Thus pits are formed onthe plastic plate when the punch is removed. The stamping action alsoexposes the plastic in the areas where the pits are formed. FIG. 10 is across sectional view which shows the relative positions of the punch andthe base plate stamped. The upper part of the figure shows the punchfacing down with the body 7 and the protrusion 8. The lower part of thefigure shows the base plate 1, the masking layer 2, and the pit 3. Theplastic plate with pits formed this way is shown in FIGS. 4 and 5 withthe base plate 1, the masking layer 2, and the pit 3. This completes thefirst step.

The base plate prepared above is then coated with the ablative material.There are several ways to coat the ablative material. Vapor depositingin vacuum or sputtering may be used. Alternatively, the ablativematerial may be dissolved in a solvent and the solution coated on thebase plate. The solution is then evaporated, leaving the ablativematerial on the plate. The ablative material may be deposited in thepits as well as on the masking layer. However, it is possible to confinethe areas where the ablative material is deposited to the pits only.This is done by using proper combination of the material for the baseplate, the material for the masking layer, and the solvent. If thematerial for the base plate has strong affinity for the solvent but thematerial for the masking layer repels the solvent, then it is possibleto wet the pitted area only, leaving the masking layer free of thesolution. This selective adhession of a solvent to predetermined area ofa surface is used extensively in lithographic printing where theprinting ink adheres to selected areas on the printing plate. The coatedbase plate is shown in FIG. 6 with the base plate 1, the masking layer2, the pit 3, and the ablative material 4.

The masking layer is then washed away in a suitable solvent, which issometimes called the stripping solution. The solvent is chosen to be thekind that dissolves the masking layer but not the ablative material.When the masking layer is washed away, any ablative material that hasbeen coated on it is also removed. The masking layer can also be removedby dissolving it chemically. Either way, the base plate is left withpits and the ablative material in each pit. This completes the secondstep. FIG. 7 shows the base plate prepared this way with the base plate1, the pit 3, and the ablative material 4.

Another plastic plate is prepared as the cover plate. The cover plate isjoined with the first plastic plate. The two may be joined by fusionwith heat or by adhessive. This completes the third step. FIG. 8 showsthe completed memory device with the base plate 1, the cover plate 5,the ablative material 4, and the empty cell 6.

An alternative to the third step described above is possible. The baseplate prepared by the first step is inverted and placed on a monomer inan uncured state. The monomer is then polymerized so that it solidifiesto form the cover plate and is joined with the first plastic plate. Amemory device with empty cells and ablative material is thus formed.

EXAMPLE 2

A plastic plate is prepared with a flat surface. The plate is coatedwith a thin layer of masking material. The masking material ispreferable softer than the plastic plate. The masking material issolvable in a stripping solution to be used later in the second step. Asin example 1, the coated base plate is shown in FIGS. 2 and 3.

A stamping punch is made of a hard metal with protrusions on it. Thelocation and shape of the protrusion correspond to the pit to be formedon the plastic plate. The punch is shown in FIG. 11 with body 17 andprotrusion 18. The protrusion in the front is shown cut in half forillustration purpose. The punch is shown facing up.

The punch is then pressed on the plastic plate. The pressure applied isonly high enough so that the protrusion on the punch penetrates themasking layer but not the plastic underneath. The stamping actionexposes the plastic in the areas where the protrusion penetrates. Butunlike example 1, no pit is formed below the masking layer by thestamping action. FIG. 12 is a cross sectional view which shows therelative positions of the punch and the base plate stamped. The upperpart of the figure shows the punch facing down with the body 17 and theprotrusion 18. The lower part of the figure shows the base plate 1, themasking layer 2, and the uncovered area 9. A perspective view of thebase plate that has been stamped this way is shown in FIG. 13 with thebase plate 1, the masking layer 2, and the uncovered area 9.

A solvent that does not dissolve the masking layer is then used topartially dissolve the uncovered surface of the plastic plate thusstamped. This forms pits in the exposed areas. The plastic plate withpits formed this way is shown in FIGS. 4 and 5. This completes the firststep.

The base plate prepared in the first step is then coated with theablative material. Again, there are several ways to coat the ablativematerial. These include vapor depositing in vacuum, sputtering, andevaporization of a solution of the ablative material. FIG. 6 shows thebase plate with the ablative material applied. The masking material isthen removed by dissolving it with a solvent or dissolving itchemically. The removal of the masking material leaves the plastic platewith pits that have ablative material in them. This completes the secondstep. FIG. 7 shows the base plate prepared this way.

Another plastic plate is prepared. The second plastic plate is joinedwith the first plastic plate. The two may be joined by fusion with heator by adhessive. This completes the third step and thus the making ofthe memory device. The completed memory device is shown in FIG. 8.

EXAMPLE 3

A glass plate is prepared with a flat surface. The plate is coated witha thin layer of masking material, such as wax or resin or their mixture.The masking material is preferable softer than the glass plate. Themasking material is solvable in a stripping solution to be used later inthe second step. As in example 1, the coated base plate is shown inFIGS. 2 and 3.

A stamping punch is made of a hard metal with protrusions on it. Thelocation and shape of the protrusion correspond to the pit to be formedon the base plate. The punch is shown in FIG. 11 with body 17 andprotrusion 18. The protrusion in the front is shown cut in half forillustration purpose. The punch is shown facing up.

The punch is then pressed on the glass plate. The pressure applied isonly high enough so that the protrusion on the punch penetrates themasking layer but not the glass underneath. The stamping action exposesthe glass in the areas where the protrusion penetrates. But no pit isformed below the masking layer by the stamping action. FIG. 12 is across sectional view which shows the relative positions of the punch andthe base plate stamped. The upper part of the figure shows the punchfacing down with the body 17 and the protrusion 18. The lower part ofthe figure shows the base plate 1, the masking layer 2, and theuncovered area 9. A perspective view of the base plate that has beenstamped this way is shown in FIG. 13 with the base plate 1, the maskinglayer 2, and the uncovered area 9.

The glass plate thus prepared are then etched. Etching can be done withhydrofluoric acid either as a vapor or as a solution in water, but alsowith an amonium fluoride or amonium bifluoride solution or any of themany known mixtures with other soluble salts in solution. The maskinglayer protects the covered area of the glass and only the uncoveredareas of the glass area are etched. Each etched area of the glass formsa pit. The base plate with pits formed this way is shown in FIGS. 4 and5. This completes the first step.

The base plate prepared in the first step is then coated with theablative material. Again, there are several ways to coat the ablativematerial. These include vapor depositing in vacuum, sputtering, andevaporization of a solution of the ablative material. FIG. 6 shows thebase plate with the ablative material applied. The masking material isthen removed by dissolving it with a solvent or dissolving itchemically. The removal of the masking material leaves the glass platewith pits that have ablative material in them. This completes the secondstep. FIG. 7 shows the base plate prepared this way.

Another glass plate is prepared. The second glass plate is joined withthe base plate. The two may be joined by fusion with heat or byadhessive.

Various methods are known in the arts for uniting two pieces of glass.The two plates may be fused together with heat. Alternatively, thesecond piece of glass can be joined with the first piece of glass withan adhesive or cement which is cured with or without heat. Sodiumsilicate, also known as water glass, is an example of such adhesive.Mixture of sodium silicate with other salt, such aluminium fluoride hasalso been used. Mixture of lead oxide and glycerine is another example.A third possibility is to coat the cover plate with a binding agent andapply heat to it while the two plates are held together. An example ofthe binding agent, known as a glass solder, is described in U.S. Pat.No. 2,615,816 by A. P. Devey, M. Manners, and J. H. Partridge. U.S. Pat.No. 3,880,632 by G. Y. Podvigalkina describes various methods of joiningtwo pieces of glass with heat, in particular, one which uses silica asbinding agent and infarad radiation to heat the binding agent.

The joining of the two pieces of glass completes the third step and thusthe making of the memory device. The completed memory device is shown inFIG. 8.

EXAMPLE 4

A flat glass plate is coated with a layer of photo resist as the maskinglayer. FIGS. 2 and 3 show the base plate coated with the photo resist.Shown in the figures are the base plate 1 and the masking layer 2 (i.e.the photo resist). The coated plate is exposed to light through aphotomask with suitable pattern on it. The exposed photo resist is thendeveloped so that certain areas of the coated layer are removed.Depending on whether the photo resist used is the positive type or thenegative type, the area removed may be the part exposed to the light orthe part not exposed. The area with the photo resist removed is thelocation where the memory cell will be located in the final product. Thecomposition of the photo resist and the method to coat and expose it arewell known in the arts of making semiconductor integrated circuit andmaking printed circuit board. The making of printing plate also uses asimilar technique. A perspective view of the base plate prepared thisway is shown in FIG. 13 with the base plate 1, the masking layer 2, andthe uncovered layer 9.

The glass plate thus prepared are then etched to form pits in theuncovered area. The base plate with pits formed this way is shown inFIGS. 4 and 5. This completes the first step.

The base plate prepared in the first step is then coated with theablative material. Again, there are several ways to coat the ablativematerial. These include vapor depositing in vacuum, sputtering, andevaporization of a solution of the ablative material. FIG. 6 shows thebase plate with the ablative material applied. The photo resist is thenremoved by dissolving it with a solvent or dissolving it chemically. Theremoval of the photo resist leaves the base plate with pits that haveablative material in them. This completes the second step. FIG. 7 showsthe base plate prepared this way.

A second glass plate is then prepared with a flat surface to cover thefirst glass plate. The two pieces of glass are joined together to formthe memory device. This completes the third step and thus the making ofthe memory device. The completed memory device is shown in FIG. 8.

EXAMPLE 5

A flat plastic plate is coated with a photo resist as the masking layer.FIGS. 2 and 3 show the base plate coated with the photo resist. Shown inthe figures are the base plate 1 and the masking layer 2 (i.e. the photoresist). The coated plate is exposed to light through a photomask withsuitable pattern on it. The exposed photo resist is then developed sothat certain areas of the coated layer are removed. The area with thephoto resist removed is the location where the memory cell will belocated in the final product. A perspective view of the base plateprepared this way is shown in FIG. 13 with the base plate 1, the maskinglayer 2, and the uncovered area 9.

A solvent that does not dissolve the photo resist is then used topartially dissolve the uncovered surface of the plastic plate thusprepared. This forms pits in the uncovered area. The plastic plate withpits formed this way is shown in Figures 4 and 5. This completes thefirst step.

The base plate prepared in the first step is then coated with theablative material. Again, there are several ways to coat the ablativematerial. These include vapor depositing in vacuum, sputtering, andevaporization of a solution of the ablative material. FIG. 6 shows thebase plate with the ablative material applied. The photo resist is thenremoved by dissolving it with a solvent or dissolving it chemically. Theremoval of the photo resist leaves the plastic plate with pits that haveablative material in them. This completes the second step. FIG. 7 showsthe base plate prepared this way.

Another plastic plate is prepared. The second plastic plate is joinedwith the first plastic plate. The two may be joined by fusion with heator by adhessive. This completes the third step and thus the making ofthe memory device. The completed memory device is shown in FIG. 8.

EXAMPLE 6

A plastic plate is prepared with a flat surface. The plate is coatedwith a thin layer of masking material. The masking material is solublein a stripping solution to be used later in the second step. The coatedplastic plate is shown in FIGS. 2 and 3.

A high power light source, preferably a laser, is focused on the surfaceof the plate to ablate the masking layer and the plastic below. The beamis focused, one after another, at the locations where the memory cellsare desired. At the location where the light beam is focused, a pit isformed. The forming of the pit by the light beam exposes the plasticbelow the masking material. The plastic plate with pits formed this wayis shown in FIGS. 4 and 5. This completes the first step.

The base plate prepared in the first step is then coated with theablative material of the memory device. Again, there are several ways tocoat the ablative material. These include vapor depositing in vacuum,sputtering, and vaporization of a solution of the ablative material.FIG. 6 shows the base plate with the ablative material applied. Themasking material is then removed by dissolving it with a solvent ordissolving it chemically. The removal of the masking material leaves theplastic plate with pits that have ablative material in them. Thiscompletes the second step. FIG. 7 shows the base plate prepared thisway.

Another plastic plate is prepared. The second plastic plate is joinedwith the first plastic plate. The two may be joined by fusion with heator by adhesive. This completes the third step and thus the making of thememory device. The completed memory device is shown in FIG. 8.

EXAMPLE 7

A plastic plate is prepared with a flat surface. The plate is coatedwith a thin layer of masking material. The masking material is solublein a stripping solution to be used later in the second step. The coatedplastic plate is shown in FIGS. 2 and 3.

A high power light source, preferably a laser, is focused on the surfaceof the plate to ablate the masking layer. The beam is focused, one afteranother, at the locations where the memory cells are desired. At thelocation where the light beam is focused, the plastic is uncovered. Aperspective view of the base plate prepared this way is shown in FIG. 13with the base plate 1, the masking layer 2, and the uncovered area 9.

A solvent that does not dissolve the masking layer is then used topartially dissolve the uncovered surface of the plastic plate thusprepared. This forms pits in the uncovered areas. The plastic plate withpits formed this way is shown in Figures 4 and 5. This completes thefirst step.

The base plate prepared in the first step is then coated with theablative material of the memory device. Again, there are several ways tocoat the ablative material. These include vapor depositing in vacuum,sputtering, and vaporization of a solution of the ablative material.FIG. 6 shows the base plate with the ablative material applied. Themasking material is then removed by dissolving it with a solvent ordissolving it chemically. The removal of the masking material leaves theplastic plate with pits that have ablative material in them. Thiscompletes the second step. FIG. 7 shows the base plate prepared thisway.

Another plastic plate is prepared. The second plastic plate is joinedwith the first plastic plate. The two may be joined by fusion with heator by adhesive. This completes the third step and thus the making of thememory device. The completed memory device is shown in FIG. 8.

EXAMPLE 8

A glass plate is prepared with a flat surface. The plate is coated witha thin layer of masking material. The masking material is soluble in astripping solution to be used later in the second step. The coated baseplate is shown in FIGS. 2 and 3.

A high power light source, preferably a laser, is focused on the surfaceof the plate to ablate the masking layer. The beam is focused, one afteranother, at each location where the memory cells are desired. At thelocation where the light beam is focused, the glass is uncovered. Aperspective view of the base plate prepared this way is shown in FIG. 13with the base plate 1, the masking layer 2, and the uncovered area 9.

The glass plate thus prepared are then etched to form pits in theuncovered areas. The glass plate with pits formed this way is shown inFIGS. 4 and 5. This completes the first step.

The base plate prepared in the first step is then coated with theablative material of the memory device. Again, there are several ways tocoat the ablative material. These include vapor depositing in vacuum,sputtering, and vaporization of a solution of the ablative material.FIG. 6 shows the base plate with the ablative material applied. Themasking material is then removed by dissolving it with a solvent ordissolving it chemically. The removal of the masking material leaves thebase plate with pits that have ablative material in them. This completesthe second step. FIG. 7 shows the base plate prepared this way.

Another glass plate is prepared. The second glass plate is joined withthe first glass plate. The two may be joined by fusion with heat or byadhesive. This completes the third step and thus the making of thememory device. The completed memory device is shown in FIG. 8.

EXAMPLE 9

This example illustrates a variation in uniting the base plate and thecover plate.

A flat glass plate is coated with a photo resist as the masking layer.FIGS. 2 and 3 show the base plate coated with the photo resist. Shown inthe figures are the base plate 1 and the masking layer 2 (i.e. the photoresist). The coated plate is exposed to light through a photomask withsuitable pattern on it. The exposed photo resist is then developed sothat certain areas of the coated layer are removed. The area with thephoto resist removed is the location where the memory cell will belocated in the final product. A perspective view of the base plateprepared this way is shown in FIG. 13 with the base plate 1, the maskinglayer 2, and the uncovered area 9.

The glass plate thus prepared are then etched to form pits at theuncovered areas. The base plate with pits formed this way is shown inFIGS. 4 and 5. This completes the first step.

The base plate prepared in the first step is then coated with theablative material. Again, there are several ways to coat the ablativematerial. These include vapor depositing in vacuum, sputtering, andevaporization of a solution of the ablative material. FIG. 6 shows thebase plate with the ablative material applied. The photo resist is thenremoved by dissolving it with a solvent or dissolving it chemically. Theremoval of the photo resist leaves the base plate with pits that haveablative material in them. This completes the second step. FIG. 7 showsthe base plate prepared this way.

A second glass plate is then prepared with a flat surface and a numberof mesas to cover the first glass plate. The mesa is a raised islandwhich serves as a spacer between the base plate and the cover plate whenthe two are joined. FIG. 14 shows the cover plate 5 with the spacers 10.The cover plate is then coated with a layer of binding agent.

The two pieces of glass are joined together with application of heat.The function of the spacer is to control the spacing between the baseplate and the cover plate. This provides space for the binding agent sothat it does not flow to other places when heat and pressure are appliedbetween the two plates.

The joining of the two pieces of glass completes the third step and thusthe making of the memory device. FIG. 15 shows the completed memorydevice with the base plate 1, the cover plate 5, the spacer 10, thebinding agent 11, the ablative material 4, and the empty cell 6.

EXAMPLE 10

This example illustrates a variation in the application of the bindingagent for uniting the base plate and the cover plate.

A flat glass plate is coated with a binding agent for uniting glass,such as the glass solder or silica described in Example 3. The plate isthen coated with a layer of photo resist as the masking layer on top ofthe binding agent. The coated plate is exposed to light through aphotomask with suitable pattern on it. The exposed photo resist is thendeveloped so that certain areas of the coated layer are removed. Thearea with the photo resist removed is the location where the memory cellwill be located in the final product.

The glass plate thus prepared are then etched to form pits in theuncovered areas. Both the binding agent and the glass of the base plateare etched. The glass plate with pits formed this way is shown in FIG.16. Shown in the figure are the base plate 1, the binding angent 11, thephoto resist 2, and the pit 3. This completes the first step.

The base plate prepared in the first step is then coated with theablative material. Again, there are several ways to coat the ablativematerial. These include vapor depositing in vacuum, sputtering, andevaporization of a solution of the ablative material. FIG. 17 shows thebase plate 1, the binding agent 11, the photo resist 2, and the ablativematerial 4. The photo resist is then removed by dissolving it with asolvent or dissolving it chemically. The removal of the photo resistleaves the base plate with pits that have ablative material in them. Thebinding agent remains on the surface of the base plate. This completesthe second step. FIG. 18 shows the base plate 1, the binding agent 11,the ablative material 4, and the pit 3.

A second glass plate is then prepared with a flat surface to cover thefirst glass plate. The two pieces of glass are joined together by heatto form the memory device.

The joining of the two plates completes the third step and thus themaking of the memory device. The completed memory device is shown inFIG. 19 with the base plate 1, the cover plate 5, the binding agent 11,the ablative material 4, and the empty cell 6.

I claim:
 1. The method of making an optical memory device comprising alight-transparent substrate having a plurality of void cells and apreselected amount of ablative material in each void cell only partlyfilling each cell such that the ablative material can be redeposited ata plurality of locations in each cell, said method comprising the stepsof applying a masking layer of coating on the surface of a base plate;mechanically stamping the coated base plate surface with a punch tocause the punch to penetrate and displace the masking layer and the baseplate underneath to form pits at preselected areas in the base plate;depositing ablative material as a coating on the surface of the maskinglayer and on the base plate in the pits such that said ablative materialfills only a portion of the volume of each of said pits; removing themasking layer and ablative layer outside of the pits by dissolving themasking coating and carrying with it the overlaying ablative material;and then laminating the base plate with a cover plate to form voidmemory cells at the pitted areas with the ablative material sealed inthe void cells to thereby form said optical memory device wherein thecover plate and base plate together function as said substrate, whereinsaid ablative material is opaque to radiant energy and is vaporizable inresponse to a high intensity radiant energy beam, and the amount ofablative material supplied to each pit is limited such that the ablativematerial can be redeposited at a plurality of locations in said cells.